This invention relates to a spinning aggregate for wrapped yarn having a drivable hollow spindle carrying a corotating sleeve with a binding yarn wound on said sleeve, a corotating positive false-twisting device into which the binding yarn and a sliver enter, said sliver being fed by means of a delivery device having a pair of delivery rollers forming a nip, and a pair of withdrawal rollers following the hollow spindle.
In the case of a known spinning aggregate for wrapped yarn of the initially mentioned type, disclosed in European Published Unexamined Patent Application (EP-OS) 67 701, an exactly defined false twist is produced by means of a positive false-twisting device, wherein the false-twisting device rotating along with the hollow spindle produces a false twist in the sliver between the false-twisting device and the delivery device during a rotation of the spindle. In order to produce a uniform wrapped yarn, it is provided in the case of the known construction that the false-twisting device is located preferably in the center between the nips of the pair of delivery rollers and the pair of withdrawal rollers, but not closer than one third of the total distance between the nips of both pairs of rollers in the direction of one of the two pairs of rollers. In practice, it has been found that despite the introduction of an exactly defined false twist and despite the maintaining of the prescribed distances, still relatively many irregularities exist in the spun yarn.
An object of the invention is to develop a spinning aggregate for wrapped yarn in such a way that the uniformity of the yarn is improved.
This object is achieved according to the invention by providing that the distance between the false-twisting device and the nip of the pair of delivery rollers is shorter than the means staple length of the sliver.
The present invention is based in part on the recognition that a false twist distance between the nip of the pair of delivery rollers and the false-twisting device that is too long results in irregularities, because the applied false twist distance is not distributed evenly over the sliver. There is the danger that thick and thin points existing in the sliver are false-twisted differently, namely that more of a false twist is introduced into the thin points than into the thick points. The thus reinforced thin and thick points will then be fixed by the binding yarn so that in the finished yarn, the previously existing slightly thick and thin points appear to an increased extent. By means of the substantial shortening of the false twist distance between the false-twisting device and the nip of the pair of delivery rollers according to the invention, an uneven introduction of the false twist is essentially prevented. In practice, it was found according to the invention that the resultant lengthening of the distance between the pair of withdrawal rcllers and the false-twisting device results in no disadvantages since in this area the sliver is already fixed by the binding yarn and is furthermore untwisted.
In the case of a spinning aggregate for wrapped yarn that is not provided with a positive false-twisting device disclosed in British Patent No. (GB-PS) 16 00 129, it is provided that the drawn sliver enters the hollow spindle at an angle of 3.degree. to 10.degree. with respect to the angle of rotation. By means of this rerouting, a false twist is produced in the sliver which, however, is not exactly defined. In addition, in the case of this type of construction, because of the lacking positive false-twisting device, the point is not exactly defined where the binding yarn winds around the sliver. Although, in the case of this known construction, the end of the hollow spindle is arranged to be very close to the nip of the pair of delivery rollers of the delivery device, whereby the distance between the end of the hollow spindle and the nip of the pair of delivery rollers is 25 mm and shorter than the staple length of the fiber material to be processed, no uniform wrapped yarn was spun in the case of this construction, as demonstrated in practice.
Preferably it is provided that the distance between the false-twisting device and the nip of the pair of delivery rollers is about 35 to 40 mm. Thus this distance is shorter than the staple of the sliver that is usually processed, but still long enough in order to possibly permit a swivelling of the hollow spindle past the pair of delivery rollers in order to interrupt the spindle drive. In this case, it is advantageous for the false-twisting device to project into the wedge-shaped gap formed by the pair of delivery rollers.
In a further development of the invention, it is provided that the false-twisting device is arranged at a short distance from the facing end of the sleeve carrying the binding yarn. In this case, it is preferably provided that the distance between the false-twisting device and the end of the sleeve carrying the binding yarn is about 10 to 15 mm. This development avoids the difficulty that, when the distance is too large, the binding yarn winds itself around the false twisting device during the withdrawal which may result not only in an impairment of the quality of the yarn but also in yarn breakage.
In a further development of the invention, it is provided that the binding yarn is wound into a cop on the sleeve, facing the false-twisting device with a slope which with respect to the axis of rotation has an angle of between 13.degree. and 40.degree. . The slope is selected corresponding to the binding yarn being used, where the angle is most often about 20.degree. with respect to the axis of rotation.
In an advantageous development of the invention, it is provided that the length of the sleeve is about three times the maximum diameter of the cop. In this case, it is advantageous if the sleeve has a length of 180 to 200 mm and if the maximum diameter of the cop is about 60 to 80 mm. By limiting the sleeve to these lengths, the problem is avoided that the binding yarn, when being pulled off the lower winding half of the cop, receives an uncontrolled additional false twist. For the same reason, it is advantageous for the diamter to be limited since otherwise the binding yarn, when being withdrawn, may graze the cop in an uncontrollable manner.
In an advantageous development of the invention, it is provided that two cross holes are provided in the proximity of the intake of the hollow spindle, which holes are disposed diametrically opposite one another and are staggered in the longitudinal direction of the hollow spindle, where these cylindrical outer surface of the hollow spindle located between the cross holes has a diameter of about 8 to 10 mm. These cross holes serve as the false-twisting device. By means of this preferred dimensioning, an advantageous compromise is found between the guiding of the binding yarn in the case of cops with (only) small diameters and a not too extensive mass at the point of the spindle.
In another development, it is provided that the hollow spindle is surrounded by a housing that is open at both ends and extends at least over the range of the sleeve up to the false-twisting device. By means of such a housing, a reduction of noise and a protection of the binding thread from influences of the environment is achieved without disturbing the operation of the spinning aggregate for yarn wrapping. Since the pair of delivery rollers that is located very close to the false-twisting device projects almost into the housoing the sliver and the binding yarn can be introduced into the false twisting device largely without disturbances.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, an embodiment in accordance with the present invention.